core: add NEXT_RUN snapshot

Added new snapshot type to save only vm configuration for the vm next run.
added also query to get vm from this configuration, and a field in vm to
mark this configuration exists.

Feature page: http://www.ovirt.org/Features/Edit_Running_VM
Change-Id: I4d68f1d7a2de9e66854985583761f47d6db553bd
Signed-off-by: Omer Frenkel <ofrenkel@redhat.com>